Nociceptive information associated with coronary artery disease is transmitted to the brain by spinothalamic and spinoreticular pathways. This project will describe the activity of spinal neurons whose axons project to supraspinal levels during experimentally initiated arrhythmias. The upper thoracic spinal cord of cats and monkeys will be explored with glass or metal microelectrodes to record extracellular activity of single cells whose axons project to the thalamus or medullary reticular formation. Once activity is recorded during somatic stimulation and electrical stimulation of the sympathetic chain, cells will be studied during the production of arrhythmias by localized electrical stimuli applied to the left or right ventricle and by coronary artery occlusion. The activity of these spinal neurons will be modified in some experiments by left stellectomy, right stellectomy, bilateral stelectomy and by electrical stimulation of the afferent vagal fibers. Vagal afferent activity often inhibits and sometimes excites spinal neurons by pathways that descend from the brainstem to the thoracic spinal cord. Previous investigators have suggested that the central nervous system has an important role in arrhythmic activity of the heart. This project will study the involvement of the central nervous system during arrhythmias and their possible modification by other visceral inputs, especially the vagal affeent descending control system.